I am running PostgreSQL *9.6.8* on AWS RDS. I'm going to try to pg-repack the table and will look to upgrade to *9.6.9* (though it's not presently available on RDS).
I just wanted to report that I found similar error "found multixact from before relminmxid" that Alexandre Arruda and Jeremy Finzel recently reported and discussed with Andres Freund. (Thanks all for good notes.)
I get this error when vacuuming a specific table in my high-transaction OLTP workload database. I am running PostgreSQL 9.5.8 on AWS RDS. I'm going to try to pg-repack the table and will look to upgrade to 9.5.9 (though it's not presently available).
